Homicide detectives Ryan Walker, Nora Houghton and Lt. Ben Carroll try to close a string of strangulation murders. Carroll and his divorced wife, Bonnie, decide to stop sleeping together. She confides in him that she's seeing another man. Walker jeopardizes the investigation when he begins seeing a conniving television reporter.

Walker is assigned to head up a task force on the strangler. Nora's brother Jack steals information and leaks it to the reporter Holly Bennett after she seduces him. Bennett places herself in harm's way when she agrees to meet the strangler. When Nora and Walt are ambushed, Nora shoots the gunman in Chinatown shoot-out, but also inadvertantly shoots and wounds Walt. This prompts Nora to consider leaving the force.

Ryan meets a woman, Robin Moore, who believes she's being stalked and may be The Strangler's next victim. She agrees to be the ""bait"" and Ryan traps The Strangler. Nora and Walt investigate the death of a man who fell out of a tenth floor window and at first it is thought to be suicide. Ben and Nora re-examine the suicide, uncovering a murder instead.

When the verdict of a man convicted seven years ago of murdering his wife is reversed, Ben risks losing his badge to gather evidence to convict him of murdering his son (whose body was never found) as well. In another case, Nora and Walt struggle with a witness who agrees to testify against the man who murdered her boyfriend but reverses her decision when the murderer escapes from jail and threatens her.

Ben and Ryan team up with Theresa Baldoni, a tough New York cop, who comes to California to catch the man who murdered another cop; only she's not interested in justice, she wants revenge. Carroll becomes romantically involved with Baldoni. Nora and Walt protect a young girl orphaned after a hit man kills her mother.

As Walt prepares to retire, he looks into a 13-year-old murder case and learns he arrested the wrong man. The department throws Walt a going-away party. Ben teams Ryan with Nora. Ryan hopes to entice Nora romantically, as they investigate a suspicious suicide. Ryan and Nora uncover that the suicide was actually a murder with a dentist for the prime suspect.

The unit investigates when a policeman is murdered in bed and quickly finds a suspect, his wife, Andie Harper! Nora worries that the murder may have been too easy. Ben concurs. The squad reopens the investigation. Ben and Ryan look at each other suspiciously, because both once had an affair with Andie Harper. They both investigate and find out how sexually voracious Andie Harper is.

Ben, Ryan and Nora investigate the apparent hate-crime murder of a Jewish boy, but discover it's more complicated and that it might have been the work of some well-off teenagers. When an unidentified beggar is murdered, Walt becomes obsessed with finding out his identity.

The whole squad is called to investigate a quadruple homicide when four people are murdered in the same apartment. In desperation, Ben turns to a psychic to find the killer.

Ben resists D.A. Simon Kingsley's pleas to arrest a teenager for murder. Ryan investigates the case. Walt runs across a multiple murderer while in the hospital for surgery.

Nora is kidnapped by jailbreaking inmates who hold her hostage as they make their way toward Mexico and feedom. The squad worries about Nora's safety among the criminals, one of whom is a serial rapist.

Ryan and Ben investigate the death of a 15-year-old call girl. Walt and Nora look into the murder of an elderly man made up to look like a suicide. Ben's wife informs him she's moving to Florida, and taking Ben's child with her.

Ryan becomes unable to resist himself as he becomes infatuated with murder suspect Grace Devlin. He continues to assert her innocence, even as evidence stack up. Ben has no choice to suspend Walker when compromising photos of him and the accused are discovered. Ben arrests Grace Devlin, but is forced to release her when one of the governor's former aides, Gil Murphy, comes forward and admits to the slaying.

Ryan, still suspended, and Nora investigate Gil Murphy's story and discover that Harris Devlin paid him a half million dollars to confess to the governor's murder. Grace, trapped in a loveless marriage and realizing Harris will never be convicted of the murder, takes matters into her own hands, poisoning herself and framing Harris for her death. Walt investigates the murder of a black high school football star.

Ben investigates a murder made to look like a suicide, with Chief Leland a main suspect. Ryan, with the aid of a phone-sex operator, looks into the possible homicide of one of her clients.